How to create a procedural embedded stone texture for ground/asphalt/pebbled concrete?
I'd recommend using Brick Texture as a core for stones generation. I've set up these nodes for some tests:


As you see I use Voronoi too (because you mentioned it) but just to shuffle the stones a little bit. I'm sure you can use noise or something else for it.

This gives us the sharp shapes we were after. We can use it as a mask then: 

I multiply it by some color, mix with another instances of this "stones texture" with a bit different sizes/frequencies/color and finally add a simple noisy background. I also apply some Image Blur from b°wide NodePack

Personally, I like it when the stones are small and I'm not sure if you'll be satisfied with it much zoomed.


I also did't manage to reach the stones density as on your 2nd image without ending with many overlapping stones.
Here's my general set-up:


UPDATE:
To make it more clear how Bricks-Voronoi pair works I'll give some more images of Bricks without its companion.
No vector input (raw boring squares):

Noise texture:

Wave texture: